I have only used Vanguard and Fidelity so I can't compare much. Fidelity is very nice and sharp, organized as well. Vanguard leaves a little to be desired but it has the necessities. How is Merrill Edge and Schwab?

I spend about 15 minutes a year actually making any changes to my investments so I haven't given it much thought. I chose:
1) Vanguard because I like their munis
2) Fidelity because my work accounts are there
I'm also considering
3) Merrill to get the credit card benefits

I've used Vanguard, Fidelty, and Schwab. IMO Schwab's website is superior in that it is more intuitive for me when browsing the site. Others may feel differently- just one mans opinion. Also very satisfied with their customer service, as well as my no pressure consultant that is assigned to me.

I prefer Vanguard, because it is easier for an older person like myself to read.

I find it highly annoying that website after website is changing over to the preschooler smart phone interface with thin pale type, creating a low contrast background which is difficult for anyone older, even with 20 20 vision, to read.

I use Vanguard, Schwab, Fidelity and TIAA regularly. I'm in the minority it seems in that I actually prefer Vanguard's site for most things. It's not fancy, but the information is displayed in a logical manner and things are generally easy to find. Fidelity's fund searching tool is pretty good considering how many funds they have to offer. Schwab's website is generally very well designed, the mobile app as well as customer service is excellent, but I find it near impossible to search for funds within their site. I usually resort to google.

I, like so many here, have Vanguard and Fidelity accounts. The latter for my and spouse’s retirement accounts. I am constantly surprised at how often Vanguard gets dinged by others for its website platform (not to mention customer service, but that is a whole other topic). I personally find Vanguard easy to navigate while Fidelity’s is much more clunky. For example, my spouse receives income from 2 separate but closely aligned sources, each with two different retirement accounts (e.g., involuntary and voluntary 403bs from one of the “employers”). When I log on to Fidelity I can really only choose to navigate to one of the four at any one time rather than see them all together. Whereas with Vanguard I can see my IRA, Roth, our taxable and kids’ UTMAs all on one page. Of course some is simply a familiarity issue as I spend considerably less time on Fidelity.

Visually, I like VG’s appearance the best. It is a very simple interface that is easy to use.
It is very bare bones for financial news and quotes, but most likely due to low ER’s.
You get just what you are willing to pay for.

I like Fido too. It is loaded with financial info and much more intuitive than VG.
Same goes for Schwab, although I detest the black section of the home screen.

TDA has the very best technology of these 4 brokers.
It seems to be geared towards traders, which I am not.
I don’t have much money with TDA, just enough to keep the account alive.
Occasionally I run the TOS platform to make an option trade but not very often.

they are all functional - whichever you are most used to.
Fidelity is simple enough once learned and almost complete (non-prototype accounts still have a number of things that could only be done in branch through paper)
Schwab I am probably not get to judge given I worked for them for 10 years and know it by working on it. functional, getting much better in terms of integration of various pieces vs SSO you to other platforms behind the scenes (401k, etc)
Vanguard is good enough